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Grand Rounds | Clinician's Corner

Near-Syncope After Exercise

Roy C. Ziegelstein, MD
JAMA. 2004;292(10):1221-1226. doi:10.1001/jama.292.10.1221.
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Published online

Syncope and near-syncope are great diagnostic challenges in medicine. On the one hand, the symptom may result from a benign condition and pose little or no threat to health other than that related to falling. On the other hand, syncope or near-syncope can be the manifestation of a serious underlying condition that poses an imminent threat to life. Patients with a cardiac cause of syncope are at far greater risk of dying in the first year after an episode of syncope or near-syncope than individuals with a noncardiac cause. A cardiac cause of syncope should be considered in every patient with syncope or near-syncope, but it is particularly common in older patients or in patients with known structural heart disease, arrhythmia, or certain electrocardiographic abnormalities. Although many diagnostic tests may be helpful in the evaluation of syncope and near-syncope, the history, physical examination, and electrocardiogram pinpoint the cause in many circumstances. Syncope after exercise may be due to left ventricular outflow tract obstruction from aortic stenosis or hypertrophic obstructive cardiomyopathy but can also suggest the diagnosis of postexercise hypotension in which an abnormality in autonomic regulation of vascular tone or heart rate results in vasodilation or bradycardia after moderate-intensity aerobic activity. The patient discussed in this case highlights the importance of the clinical history in the evaluation of this condition, since the diagnosis was revealed as the patient's story was described and eventually acted out.

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Figure 1. Location of the Carotid Sinus
Graphic Jump Location
The carotid sinus is a small dilatation of the internal carotid artery immediately above the bifurcation of the common carotid artery that contains specialized sensory nerve endings sensitive to pressure or stretch. To perform carotid sinus massage, firm but gentle pressure is applied to the area at the midpoint between the angle of the mandible and the superior border of the thyroid cartilage along the anterior margin of the sternocleidomastoid muscle.
Figure 2. Types of Responses to Carotid Sinus Massage in Carotid Sinus Hypersensitivity
Graphic Jump Location
A, A pure cardioinhibitory response produces a reflex slowing of the heart and may produce sinus arrest or asystole. A fall in systolic blood pressure typically occurs deriving from and proportional to the extent and duration of the decrease in heart rate. During carotid sinus massage, a positive cardioinhibitory response is defined as a ventricular pause of more than 3 seconds. If the slowing of the heart is prevented (for example with a pacemaker), individuals exhibiting a pure cardioinhibitory response will not experience a decline in blood pressure. B, A pure vasodepressor response produces hypotension without bradycardia due chiefly to inhibition of sympathetic vasoconstriction. A pure vasodepressor response results in a decline in systolic blood pressure that is of longer duration than that observed in a pure cardioinhibitory response. During carotid sinus massage, a positive vasodepressor response is defined as a decline in the systolic blood pressure of 50 mm Hg or greater. Note that about a third of individuals demonstrate both types of hypersensitivity responses.




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